Scholarly Open Access repositories contain lots of treasures including rare or otherwise unpublished materials and articles that scholars self-archive, often as part of their institution's mandate. But it can be hard to discover this material unless users know exactly where to look. Since the very beginning, libraries have played a major role in supporting the OA movement. Next to all services they can provide to support the deposit of research output in the repositories, they can make Open Access materials widely discoverable by their patrons through general search engines (Google, Bing...), specialized search engines (like Google Scholar) and library discovery tools, thus expanding their collection to include materials that they would not necessarily pay for. In this paper, we intend to focus on two aspects regarding Open Access and Primo discovery tool. In early 2013, Ex Libris Group started to add institutional repositories to Primo Central Index (PCI), their mega-aggregation of hundreds of millions of scholarly e-resources. After 2 years, it may be interesting to take stock of the current situation of PCI regarding Open Access institutional repositories. On basis of a survey to carry out among the Primo community, the paper also shows how libraries using Primo discovery tool integrate Green Open Access contents in their catalog. Two major ways are possible for them: Firstly, they can directly harvest, index and manage any repository in their Primo and display those free contents next to the more traditional library collections; Secondly, if they are PCI subscribers, they can quickly and easily activate any, if not all, of the Open Access repositories contained PCI, making thus the contents of those directly discoverable to their end users.